What is "virtual public" keyword?

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I've seen some strange code below.

C++

class AA
{};
class BB: virtual public AA
{};

What is the "virtual public" means? And there it can be changed into "virtual private" and "virtual protected"?

If so, what is the difference between them?

Anyone notice me.

Posted 3-Jul-14 17:54pm

WuRunZhe

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PIEBALDconsult 4-Jul-14 0:08am

Virtual and public are two different things.

WuRunZhe 4-Jul-14 2:17am

Yes, you're right. But how can you explain of that? "Virtual" keyword is used at inheritance.

Sergey Alexandrovich Kryukov 4-Jul-14 1:06am

There is no such thing. I doubt someone would seriously volunteer to explain you those two concepts. It looks like you are trying to code by trial-and-error method, not understanding what you are writing. It never works. You need to read a book on OOP to understand "virtual". It can be explained in one article, but only to the people who has serious background in many other aspects of programming. And such people who are literate but never understood how OOP works usually become highly surprised/excited. So, grab a book and start learn something serious.

Sorry for not answering the question. I have serious reasons not to do it. And I think my advice above will be much better for you.

—SA

WuRunZhe 4-Jul-14 2:16am

You mean, "virtual" keyword could not be used like that?

Sergey Alexandrovich Kryukov 4-Jul-14 2:28am

Sorry, I did not realize what is your concern; but you also wasn't clear and correct in this question. Now, I can answer your question.
—SA

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Sergey Alexandrovich Kryukov · Accepted Answer · 2014-07-03T20:27:00

Solution 1

This specific use of virtual is related to quite a delicate feature of C++, specific to C++, called virtual base classes. You can understand how it works from this chapter of this manual:
http://www.learncpp.com/cpp-tutorial/118-virtual-base-classes[^].

This is some kind of complexity related to C++ multiple inheritance. When you have the same inherited members in more then one inheritance path on the inheritance graph, their meaning could be ambiguous. C++ offers two ways to derive from a base class, two options for inheritance.

—SA

Posted 3-Jul-14 20:27pm

Sergey Alexandrovich Kryukov

Updated 3-Jul-14 20:31pm

v3

Comments

WuRunZhe 4-Jul-14 2:35am

Thank you for your answer. I've understood about it very clearly.

Sergey Alexandrovich Kryukov 4-Jul-14 3:01am

That's great. My pleasure.
—SA

CPallini 4-Jul-14 2:49am

5.

Sergey Alexandrovich Kryukov 4-Jul-14 3:01am

Thank you, Carlo.
—SA